Polyamides or “nylons” are polymers used to make a wide variety of consumer goods, including women's stockings, parachutes, ropes, and components of tires. One disadvantage of polyamides is that when they are exposed to flame they can break down to form hazardous ash and fumes. For uses that may include exposure to flame it is therefore important to improve the flame retardancy of polyamides and their blends with other polymers.
Blending polyamides with poly(arylene ether)s can improve the flame retardancy of the polyamide and also improve some physical properties. However, the improvement in flame retardancy is not sufficient for many applications. Accordingly, considerable effort has been directed to identifying additives that can improve the flame retardancy of polyamide and polyamide/poly(arylene ether) blends without unduly compromising their desirable physical properties.
In one approach, metal dialkylphosphinate flame retardants have been used to improve the flame retardancy of polyamide/poly(arylene ether) blends. See, for example, U.S. Pat. No. 7,534,822 to Elkovitch et al., and U.S. Pat. No. 7,592,382 to Borade et al. Although metal dialkylphosphinates have been demonstrated to improve the flame retardancy of polyamide/poly(arylene ether) blends, relatively large amounts are needed to achieve a high flame retardancy rating, such as a UL 94 V-0 rating. Use of such large amounts of metal dialkylphosphinates is expensive and is accompanied by a degradation in physical properties of the polymer blend. Use of large amounts of metal dialkylphosphinate flame retardants also increases the density (specific gravity) of the blends, thereby discouraging their use to form parts for automotive use and other weight-sensitive applications.
In another approach, blends of brominated polymers and antimony trioxide are used to improve the flame retardancy of polyamides. See, for example, Japanese Patent Application Publication Nos. JP 10-168307A of Yakabe et al., and JP 2000-281896 A of Endo et al. Relatively large amounts of the brominated polymers and antimony trioxide are required, the physical properties of the blends are degraded, and the density of the blends is increased.
There therefore remains a need for polyamide/poly(arylene ether) blends that exhibit an improved balance of flame retardancy, physical properties, density, and cost.